Table 2. Kinetic parameters for side-chain cleavage of 7-DHC and cholesterol by bovine and human cytochromes P450scc.
Kinetic parameters were determined with substrates and P450scc incorporated into phospholipid (PL) vesicles prepared from dioleoyl phosphatidylcholine containing 15 mol% cardiolipin. Values for kcat and Km are ± SE and are expressed as min−1 and mol sterol·mol PL−1, respectively. They were obtained from fitting hyperbolic curves to the kinetic data using KALEIDAGRAPH.
| Human P450scc
|
Bovine P450scc
|
|||||
|---|---|---|---|---|---|---|
| Substrate | Km | kcat | kcat/Km | Km | kcat | kcat/Km |
| Cholesterol | 0.164 ± 0.009 | 19.0 ± 0.4 | 116 | 0.078 ± 0.011 | 39.3 ± 1.7 | 504 |
| 7-DHC | 0.103 ± 0.006 | 13.3 ± 0.4 | 129 | 0.069 ± 0.010 | 24.4 ± 1.1 | 353 |